Function and performance of the hottest cutting gr

2022-08-20
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The function and performance of cutting (grinding) fluid

cooling effect of different cooling and lubricating materials

in the process of metal cutting, in order to improve the cutting efficiency, improve the accuracy of the workpiece and reduce the surface roughness of the workpiece, prolong the service life of the tool, and achieve the best economic effect, it is necessary to reduce the friction between the tool and the workpiece, the tool and the chip, and take away the heat generated by material deformation in the cutting area in time. To achieve these goals, on the one hand, the machining rate of metal cutting is rapidly improved by developing tool materials with high hardness and high temperature resistance and improving the geometry of tools, such as the advent of tool materials such as carbon steel, high-speed steel, cemented carbide and ceramics, as well as the use of indexable tools; On the other hand, using cutting (grinding) fluid with excellent performance can often significantly improve the cutting efficiency, reduce the surface roughness of the workpiece, prolong the service life of the tool, and achieve good and economic benefits. The functions of cutting fluid are as follows:

1 Cooling effect

cooling effect is to take cutting heat away from solids (tools, workpieces and chips) by convection heat transfer and vaporization of cutting fluid, reduce the temperature of cutting area, reduce workpiece deformation, and maintain tool hardness and size

the cooling effect of cutting fluid depends on its thermal parameters, especially its specific heat capacity and thermal conductivity. In addition, the flow conditions and heat exchange coefficient of liquid also play an important role. The heat exchange coefficient can be improved by changing the surface active materials and the heat of vaporization. Water has high specific heat capacity and large thermal conductivity, so the cutting performance of water-based cutting fluid is better than that of oil-based cutting fluid. The table shows the executive parameter values of water and oil

thermal parameter value category of surface water and oil thermal conductivity

w/(m.k) specific heat capacity

j/kg K vaporization heat

j/g water 0.634.18 × Oil 0.125~0.211.67~2.09 × 103167~314

changing the flow conditions of the liquid, such as increasing the flow rate and increasing the flow rate, can effectively improve the cooling effect of the cutting fluid, especially for the oil-based cutting fluid with poor cooling effect, increasing the supply pressure and increasing the flow rate of the cutting fluid can improve the cooling performance. This method is used in gun drilling deep holes and high-speed gear hobbing. Using spray cooling, the liquid is easy to vaporize, and the cooling effect can be significantly improved. In cutting, the cooling effect of different cooling and lubricating materials is shown in the figure

figure cooling effect of different cooling and lubricating materials

the cooling effect of cutting fluid is affected by the permeability of cutting fluid. Cutting fluid with good permeability has a fast cooling speed for the blade, and the permeability of cutting fluid is related to the viscosity and wettability of cutting fluid. The permeability of low viscosity liquid is better than that of high viscosity liquid, the permeability of oil-based cutting fluid is stronger than that of water-based cutting fluid, and the permeability of water-based cutting fluid containing surfactant is greatly improved. The wettability of cutting fluid is related to the surface tension of cutting fluid. When the surface tension of the liquid is high, the liquid expands and gathers into droplets on the surface of the solid, and the permeability of this liquid is poor; When the liquid surface tension is small, the liquid expands around the solid surface, and the contact angle of solid liquid gas is very small, or even zero. At this time, the permeability of the liquid is good. The liquid can quickly expand into the gap between the tool and the workpiece, and between the tool and the chip, which can enhance the cooling effect

the cooling effect is also related to foam. Because the interior of foam is air, the thermal conductivity of air is poor, and the cutting fluid with more foam is cold, but the effect will be reduced due to the relatively high product cost. Therefore, generally, synthetic cutting fluid containing surfactant is added with a small amount of emulsified silicone oil to play the role of defoaming. Recent studies have shown that ionic water-based cutting fluid can quickly eliminate the static charge generated by strong friction during cutting and grinding through the reaction of ions, so that the workpiece does not produce high heat and has a good cooling effect. This kind of ionic cutting fluid has been widely used as a cooling lubricant for high-speed grinding and strong grinding

2. Lubrication

in cutting, there is friction between tools and cutting, between tools and workpiece surface, and cutting fluid is the lubricant to reduce this friction

in terms of tools, because the tool has a back angle in the cutting process, its contact part with the processed material is less than that of the rake face, and the contact pressure is also low. Therefore, the friction and lubrication state of the rake face is close to the boundary lubrication state. Generally, substances with strong adsorption, such as oily agents and extreme pressure agents with reduced shear strength, can effectively reduce friction. The condition of the rake face is different from that of the rear face. The deformed cutting in the shear zone is forced to extrude under the push of the tool, and its contact pressure is large. The cutting also reaches high temperature due to plastic deformation. After the cutting fluid is supplied, the cutting also shrinks due to sudden cooling, which reduces the contact length between the tool and the chip on the rake face and the metal contact area between the chip and the tool, and also reduces the average shear stress, This leads to the increase of the shear angle and the reduction of the cutting force, so that the cutting performance of the workpiece material is improved

in the grinding process, after adding the grinding fluid, the grinding fluid infiltrates into the friction between the abrasive particles and the workpiece and between the abrasive particles and the debris to form a lubricating film. Because of this lubricating film, the friction of these interfaces is reduced, so as to prevent the friction and wear of the abrasive cutting edge and reduce the surface roughness of the workpiece

the lubricating effect of cutting fluid is generally better than that of water-based cutting fluid, and the effect of oil-based cutting fluid containing oiliness and extreme pressure additives is better. Oily additives are generally long-chain organic compounds with extreme pressure groups (), such as higher fatty acids, higher alcohols, animal and vegetable fats, etc. Oil based additives form a lubricating film on the surface of metal through the adsorption of polar groups, so as to reduce the friction between tools and workpiece, tools and chips, so as to reduce the cutting resistance, prolong the service life of tools, and reduce the roughness of workpiece surface. The function of oil additives is limited to the condition of low temperature. When the temperature exceeds 200 ℃, the adsorption layer of oil additives is damaged and loses its lubrication function. Therefore, generally, cutting fluid containing oil additives is used for low-speed and precision cutting, while cutting fluid containing extreme pressure additives should be used for high-speed and heavy cutting

the so-called extreme pressure additives are some compounds containing sulfur, phosphorus and chlorine elements. These compounds react with metals at high temperature to produce iron sulfide, iron phosphide, iron chloride and other substances with low shear strength, so as to reduce the cutting resistance, reduce the friction between tools and work pieces, tools and chips, and make the cutting process easy. The cutting fluid containing EP additives can also inhibit the formation of chip nodules and improve the surface roughness of the workpiece. The table shows the properties of solid lubricating film generated by sulfur and chlorine extreme pressure additives

the table shows the properties of the solid lubricating film generated by sulfur and chlorine extreme pressure additives. The melting point (℃) shear strength (%) of the solid lubricating film crystalline structure fefes119350fe (15) + FES (85) alloy 985feci267220 layered lattice feci3302 layered lattice

it can be seen from the table that the crystallization of ferric chloride is layered structure, so the shear strength is the lowest. Compared with iron sulfide, ferric chloride has a low melting point and will lose its lubricating effect at high temperature (about 400 ℃). Iron phosphate is between iron chloride and iron sulfide, and iron sulfide has the best high temperature resistance (700 ℃). Cutting fluid containing sulfur extreme pressure agent is generally used in heavy-duty cutting and machining of difficult cutting materials. The effective temperature range of cutting fluid additives is shown in the figure

figure the temperature range of the effective effect of cutting fluid additives

EP additives have the same effect on non-ferrous metals such as copper and aluminum, in addition to reacting with ferrous metals such as steel and iron to produce a lubricating film with low shear strength in China's Plastic Machinery Market. However, active extreme pressure additives should not be used in the cutting of non-ferrous metals to avoid corrosion to the workpiece. The table shows the characteristics of the reactants formed by the action of cutting fluid containing extreme pressure additives with different metals

the table shows the characteristics of the reactants formed by the action of cutting fluid containing extreme pressure additives with different metals, two-dimensional cutting, t=0.05mm, υ= 5.5m/min, high speed steel, a=15 ° shear strength of processed material metal

MPa shear strength of cutting fluid reaction products reaction products ζ 1

MPa friction reduction rate

% friction reduction rate obtained from the test

% iron 1305 carbon tetrachloride

alkyl sulfur feclfecl315288fes

FeS2 copper 941 carbon tetrachloride

alkyl sulfur CuCl

cu2s102

4189

5765

55 aluminum 402 carbon tetrachloride ALCL

the lubricating effect of cutting fluid is the same as that of cutting.Cutting fluid with good permeability, Lubricant can penetrate into the interface between chip and tool and the interface between tool and workpiece in time, forming lubricating film on the surface of chip, workpiece and tool, reducing friction coefficient and cutting resistance

in addition to the above lubrication effect, recent studies believe that cutting can directly penetrate into the micro cracks on the metal surface, changing the physical properties of the processed material, thereby reducing the cutting resistance and making the cutting process easy

3. Cleaning effect

in the process of metal cutting, cutting, iron powder, grinding debris, oil dirt and other things are easy to adhere to the surface of the workpiece, tools and grinding wheels, affecting the cutting effect, and making the workpiece and machine tools dirty and difficult to clean, so the cutting fluid must have a good cleaning effect. For oil-based cutting fluid, the lower the viscosity, the stronger the cleaning ability, especially the cutting fluid containing light components such as diesel oil and kerosene, the better the penetration and cleaning performance. Generally speaking, water-based cutting fluid containing surfactant has better cleaning effect. On the one hand, surfactant can adsorb all kinds of particles and oil sludge, and form an adsorption film on the surface of the workpiece to prevent particles and oil sludge from adhering to the workpiece, cutting tools and grinding wheels. On the other hand, it can penetrate into the interface between particles and oil dirt, separate particles and oil dirt from the interface, and take them away with the cutting fluid, so as to play a cleaning role. The cleaning effect of cutting fluid should also be manifested in the good separation and sedimentation of chips, grinding, iron powder, oil, etc. After the recycled cutting fluid returns to the cooling tank, it can quickly make the cuttings, iron powder, wear debris, particles, etc. settle at the bottom of the container, and the oil dirt and other substances are suspended on the liquid surface, so as to ensure that the cutting fluid can remain clean after repeated use, ensure the processing quality and extend the service life

4. Rust prevention

in the process of cutting, if the workpiece is in contact with the corrosive medium produced by the decomposition or oxidative deterioration of water and cutting fluid, such as sulfur, sulfur dioxide, chloride ion, acid, hydrogen sulfide, alkali, etc., it will be corroded, and the parts in contact with the cutting fluid of the machine tool will also be corroded. After the workpiece is processed or during the storage between processes, if the cutting fluid does not have certain rust prevention ability, The workpiece will be eroded by water in the air and corrosive media to produce chemical corrosion and electrochemical corrosion, causing the workpiece to rust. Therefore, it is required that the cutting fluid must have good rust prevention performance, which is one of the most basic properties of the cutting fluid. Generally, cutting oil has certain antirust ability. If the storage period between processes is not long, antirust additives can not be added, because adding antirust additives such as barium petroleum sulfonate to cutting oil will reduce the anti-wear performance of cutting oil. If cutting oil with good rust resistance is required, 0.1% - 0.3% dodecenylsuccinic acid can be added. Cutting oil that requires no corrosion to copper can be added with 0.2%~0.3% benzotriazole, which can effectively prevent the discoloration and corrosion of copper

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